The present invention relates to a centering unit for a color television camera apparatus having plural pick-up tubes.
Two methods for centering of a three tube color television camera are generally known. The first method uses a specific test chart to produce a centering correction voltage which corresponds to the phase difference between video signals of two channels, i.e., green and red, or green and blue channels. This method is disclosed in Japanese Patent Publication No. 51-3453. In this method, however, a predetermined test pattern must be picked up. This hinders the smooth operation of television camera apparatus, particularly in the case of portable television camera apparatus.
A second method is disclosed in the paper entitled "Automatic Centering Unit for the Registration of a Color Television Camera," Jour. SMPTE, 81: 4-13, January 1972. This method is performed without a specific test chart. In the second method, leading (or trailing) edges contained in video signals of two channels are extracted, respectively, and compared with each another so as to produce the centering correction signal. This system has a drawback that erroneous operation is likely when a video signal is not sufficiently focused, has a low level portion, or contains noise, since the system uses an arbitrary video signal for producing the centering correction signal. In view of this, in order to prevent the erroneous operation, the centering operation in this method is performed at an extremely slow control speed to prevent temporary error data. Therefore, this control method requires a long control time. Alternatively, there is employed a circuit for ceasing the control when amounts of error at positions displaced from each other by a given distance in one picture (field) are not equal. In order to lessen the possibility of the occurance of erroneous operation by this method, however, it is necessary to compare various error amounts at various positions in the field to decide whether the control is performed. This has the drawbacks that a circuit arrangement is complicated, and there is the possibility that the centering adjustment is scarcely actually controlled.